The use of information technology by increasingly wide segments of the population imposes strict usability requirements and has created complex application areas, such as, for example, that of providing answers to inaccurate questions or interactively using computer-based education and learning aids. One limit to the extensive use of modern voice synthesis and recognition technology is related to the limit level of naturalness permitted by the interfaces by means of which human users interact with a computer-based system. Reference to software modules for developing interfaces supporting a certain limit degree of initiative by users (starting from a generic voice prompt) are found in the prior art and in patents in the field of human-machine interfaces. Users can interact with current off-the-shelf systems by either answering precise questions or choosing from a set prompted by the system. This type of interaction is not very natural and is disliked by system users.
Furthermore, this type of interaction is not very practicable in application contexts where an explicit model of the user's vision of the service cannot be provided and for which it may consequently be difficult to envisage descriptions of the various linguistic utterances that the user may use to express such a vision. This restriction limits system use, on one hand, and drastically curtails the possible areas in which information technology can be used. Access to data and information by increasingly wide segments of the user population must be based on the availability of natural interfaces, capable of giving the user the necessary freedom of expression to respond in a concise way without needing to necessarily use the utterances prompted by the system. System usability is also entrusted to the user's possibly of correcting information that may not have been understood by the natural language recognition and analysis modules. Furthermore, today's suppliers of automatic information systems need to respond to the needs of clientele who require access to services using their own natural language (we will refer to this requirement as “multilingual”).
Some dialogue system prototypes currently available at universities and research centers support this type of interaction but commercial applicability is affected by the need to redefine considerable amounts on information whenever the system is carried across to a new application domain and/or to a new language. This means that the costs of real application can hardly be supported by language industries and potential users.